Universe – Size and Age

I posted this question that was bothering me when I read that they found a galaxy at about 13 billion light years away. My understanding of that statement is: At distance of 13 billion light years, there was a galaxy 13 billion years ago, so that we can see the light from it now. Wouldn’t that mean that the universe is at least 26 billion years old? It must have taken the galaxy about 13 billion years to reach where it appears to be, and the light from it must take another 13 billion years to reach us.

In answering my question, Martin and Swansont (who I assume are academic phycisists) point out my misconceptions and essentially ask me to learn more. All shall be answered when I’m assimilated, it would appear! 🙂

This debate is published as a prelude to my post on the Big Bang theory, coming up in a day or two.

Mowgli

03-26-2007 10:14 PM

Universe – Size and Age

I was reading a post in http://www.space.com/ stating that they found a galaxy at about 13 billion light years away. I am trying to figure out what that statement means. 对我来说，, it means that 13 billion years ago, this galaxy was where we see it now. Isn’t that what 13b LY away means? 如果是这样的, 那不是意味着宇宙是至少,,en,整个宇宙从一个奇点开始,,en,怎么会这样的星系是它在哪里,,en,十亿年前，除非它至少有,,en,十亿年才能到达那里,,en,暂时忽略通胀阶段,,en,我听到有人解释说，空间本身正在扩大,,en,这是什么意思,,en,是不是只是一种说法，认为光的速度是较小的，前一段时间的华丽的方式,,en,swansont,,en,引用,,en,最初发布者,,en,忽略所有的休息,,en,怎么会变成这样意味着宇宙,,en,光速是原子结构的固有部分,,en,在精细结构常数,,en,如果c的变化,,en,然后原子光谱的图案必须改变,,en,目前还没有任何证实的数据显示，甲型已经改变,,en 26 billion years old? 我的意思是, the whole universe started from one singular point; how could this galaxy be where it was 13 billion years ago unless it had at least 13 billion years to get there? (Ignoring the inflationary phase for the moment…) I have heard people explain that the space itself is expanding. What the heck does that mean? Isn’t it just a fancier way of saying that the speed of light was smaller some time ago?

swansont

03-27-2007 09:10 AM

Quote:

Originally Posted by Mowgli (Post 329204)

我的意思是, the whole universe started from one singular point; how could this galaxy be where it was 13 billion years ago unless it had at least 13 billion years to get there? (Ignoring the inflationary phase for the moment…)

Ignoring all the rest, how would this mean the universe is 26 billion years old?

Quote:

Originally Posted by Mowgli (Post 329204)

I have heard people explain that the space itself is expanding. What the heck does that mean? Isn’t it just a fancier way of saying that the speed of light was smaller some time ago?

The speed of light is an inherent part of atomic structure, in the fine structure constant (alpha). If c was changing, then the patterns of atomic spectra would have to change. There hasn’t been any confirmed data that shows that alpha has changed (出现了不定期文件声称它,,en,但你需要有人重复测量,,en,剩下的是所有没有变化一致,,en,马丁,,en,要确认或加强什么swansont说,,en,有猜测和涉及c更改随着时间的推移一些边缘或非标准的宇宙观,,en,或α随时间变化的,,en,但不断变化的常数的事情只是变得越来越裁定out.I've一直看超过,,en,年，越来越多的人看，研究证据的可能性就越小，似乎有什么变动,,en,他们用自己data.So排除这种可能性越来越精确它可能是最好忽略,,en,变化的光的速度,,en,直到宇宙学是一个非常熟悉的标准宇宙学的主流,,en,你有误解无忌,,en,理论,,en,胜过特别版本,,en, but you need someone to repeat the measurements), and the rest is all consistent with no change.

Martin

03-27-2007 11:25 AM

To confirm or reinforce what swansont said, there are speculation and some fringe or nonstandard cosmologies that involve c changing over time (or alpha changing over time), but the changing constants thing just gets more and more ruled out.I’ve been watching for over 5 years and the more people look and study evidence the LESS likely it seems that there is any change. They rule it out more and more accurately with their data.So it is probably best to ignore the “varying speed of light” cosmologies until one is thoroughly familiar with standard mainstream cosmology.You have misconceptions Mowgli

General Relativity (该 1915 theory) trumps Special Rel (1905)

他们实际上并不矛盾，如果你正确地理解他们,,en,因为SR只有非常有限的当地适用性,,en,喜欢飞船路过,,en,只要GR和SR似乎矛盾,,en,相信GR,,en,这是比较全面的理论,,en,GR没有对距离非常远可以提高速率的速度极限,,en,唯一的限速是当地的东西,,en,你不能赶上，并通过光子,,en,因此，我们能够而且确实观察到的东西，是从我们更为快速的消退比C,,en,那会很远,,en,SR不适用。,,en,这是一个科学上午的文章，我认为去年在解释,,en,谷歌作者的名字查尔斯·莱恩威弗和塔玛拉·戴维斯,,en,我们知道很多东西，是目前超过,,en,十亿LY远,,en, because SR has only a very limited local applicability, like to the spaceship passing by:-)

Wherever GR and SR SEEM to contradict, believe GR. It is the more comprehensive theory.

GR does not have a speed limit on the rate that very great distances can increase. the only speed limit is on LOCAL stuff (you can’t catch up with and pass a photon)

So we can and DO observe stuff that is receding from us faster than c. (It’s far away, SR does not apply.)

This was explained in a Sci Am article I think last year

Google the author’s name Charles Lineweaver and Tamara Davis.

We know about plenty of stuff that is presently more than 14 billion LY away.

Also a “singularity” does not mean a single point. that is a popular mistake because the words SOUND the same.

A singularity can occur over an entire region, even an infinite region.

Also the “big bang” model doesn’t look like an explosion of matter whizzing away from some point. It shouldn’t be imagined like that. The best article explaining common mistakes people have is this Lineweaver and Davis thing in Sci Am. I think it was Jan or Feb 2005 but I could be a year off. Google it. Get it from your local library or find it online. Best advice I can give.

Mowgli

03-28-2007 01:30 AM

To swansont on why I thought 13 b LY implied an age of 26 b years:When you say that there is a galaxy at 13 b LY away, I understand it to mean that 13 billion years ago my time, 星系是在那里我看到现在的地步,,en,b LY远离我,,en,明知一切从相同点开始,,en,它必须采取至少星系,,en,b年来获得它在哪里,,en,b年前,,en,我敢肯定，我一定是wrong.To马丁,,en,我需要学习相当多的关于宇宙学,,en,但你提到的几件事情让我感到吃惊,,en,我们如何观察到的东西，是从作为FTL后退,,en,不会相对论多普勒频移式给出假想1个 Z,,en,而超越的东西,,en,他们是,,en,外,,en,我一定会抬头看你提到的作者,,en,我敢肯定，我一定是错的,,en,这将取决于你怎么做你的校准,,en,只是看着多普勒频移，而忽略其他影响因素,,en,如果你知道，速度与距离相关,,en (which is 13 b LY away from me). Knowing that everything started from the same point, it must have taken the galaxy at least 13 b years to get where it was 13 b years ago. 所以 13+13. I’m sure I must be wrong.To Martin: 你是对的,,en,还有更多的这种思路的不仅仅是暴和AGN飞机,,en,续集本文,,en,讨论了一些含义,,en,但这部续集太投机得到发表在什么像样的杂志,,en,我跟我的日常工作太忙，担心这些事情,,en,但是我希望要回物理学,,en,并且可能还要理念,,en,在几年,,en,干杯,,en, I need to learn quite a bit more about cosmology. But a couple of things you mentioned surprise me — how do we observe stuff that is receding from as FTL? 我的意思是, wouldn’t the relativistic Doppler shift formula give imaginary 1 z? And the stuff beyond 14 b LY away – are they “outside” 宇宙?I will certainly look up and read the authors you mentioned. 谢谢.

swansont

03-28-2007 03:13 AM

Quote:

Originally Posted by Mowgli (Post 329393)

To swansont on why I thought 13 b LY implied an age of 26 b years:When you say that there is a galaxy at 13 b LY away, I understand it to mean that 13 billion years ago my time, 星系是在那里我看到现在的地步,,en,b LY远离我,,en,明知一切从相同点开始,,en,它必须采取至少星系,,en,b年来获得它在哪里,,en,b年前,,en,我敢肯定，我一定是wrong.To马丁,,en,我需要学习相当多的关于宇宙学,,en,但你提到的几件事情让我感到吃惊,,en,我们如何观察到的东西，是从作为FTL后退,,en,不会相对论多普勒频移式给出假想1个 Z,,en,而超越的东西,,en,他们是,,en,外,,en,我一定会抬头看你提到的作者,,en,我敢肯定，我一定是错的,,en,这将取决于你怎么做你的校准,,en,只是看着多普勒频移，而忽略其他影响因素,,en,如果你知道，速度与距离相关,,en (which is 13 b LY away from me). Knowing that everything started from the same point, it must have taken the galaxy at least 13 b years to get where it was 13 b years ago. 所以 13+13. I’m sure I must be wrong.

That would depend on how you do your calibration. Looking only at a Doppler shift and ignoring all the other factors, if you know that speed correlates with distance, you get a certain redshift and you would probably calibrate that to mean 13b LY if that was the actual distance. That light would be 13b years old.

But as Martin has pointed out, space is expanding; the cosmological redshift is different from the Doppler shift. Because the intervening space has expanded, AFAIK the light that gets to us from a galaxy 13b LY away is not as old, because it was closer when the light was emitted. I would think that all of this is taken into account in the measurements, so that when a distance is given to the galaxy, it’s the actual distance.

Martin

03-28-2007 08:54 AM

Quote:

Originally Posted by Mowgli (Post 329393)

I will certainly look up and read the authors you mentioned.

This post has 5 或 6 links to that Sci Am article by Lineweaver and Davis